Flavanols are members of a larger family of compounds called polyphenols. These contain more than one hydroxyl group (OH) bonded to the corresponding benzene ring. Oligomeric flavenols include procyanidines and prodelfinidines depending on whether these present two or three hydroxyl groups in the B ring of the flavenolic structure, respectively. FIG. 1 shows the general structure of procyanidines and prodelfinidins. Polyphenols and, more specifically, flavenols are present in all aerial parts of plants and are found in high concentrations in skin, bark and seeds. Sources rich in polyphenols are leaves of the tea plant, grape skin/pips and pine bark. The antioxidant/antitiradical action of polyphenols makes them useful as products for the prevention of diseases and health promotion. Body cells are constantly exposed to so-called reactive oxidant species (ROS) such as hydrogen peroxide (H2O2), superoxide anion (O2+−), hydroxyl radical (OH+) and peroxide radicals (ROO+), which have the potential to cause cellular damage. For example, damage of genetic material (DNA) can cause mutations and cancer, and alterations in blood proteins (low-density lipoproteins, LDL) can lead to lipid accumulation and consequent blockage of arteries. In the skin, lipidic oxidation of the cell wall is related to changes in permeability which cause dryness and premature aging. Most ROS are produced during ordinary biological processes and the organism avoids these harmful effects using its own defense mechanisms (e.g. superoxide dysmutase, catalase and glutathione peroxidase against superoxide anion, hydrogen peroxide and organic peroxides, respectively). However, defense systems are not perfect and some of the reactive oxidant species can evade these. Moreover, some diseases, aging or external factors such as environmental pollution, tobacco and ultraviolet radiation can produce ROS levels that exceed the defense mechanisms' capacity. In these cases, an additional preventive action is required using exogenous antioxidants. For information about ROS, oxidative damage, defense mechanisms and the function of polyphenols and other antioxidants, see Diplock, A. T., Charleux, J. L., Crozier-Willi, G., Kok, F. J., Rice-Evans, C., Roberfroid, M., Stahl, W., Vina-Ribes, J., Br. J. Nutr., 80 Suppl 1, 77-112 (1998). Natural extracts of procyanidine have been described with antioxidant activity [Pietta, P., Simonetti, P., Mauri, P., J. Agr. Food Chem., 46 (11), 4487-4490 (1998); Masquellier, J., U.S. Pat. No. 4,698,360; Frangi, E., Bertani, M., Mustich, G., Tuccini, G., U.S. Pat. No. 5,484,594; Nafisi-Movaghar, K., Seroy, W. A., Svanoe, T. T., U.S. Pat. No. 5,912,363] and some of these are currently on the market.
Polyphenols also present other interesting activities, some of which are related with their adhesive/antiadhesive properties. Hence, polyphenols and especially oligomeric flavenols and glycosylated flavenols present antimicrobial activity at least partially due to inhibition of bacterial adhesion Walker, E. B., Mickelsen, R. A., Mickelsen, J., U.S. Pat. No. 5,646,178; Walker, E. B., Mickelsen, R. A., Mickelsen, J., U.S. Pat. No. 5,650,432; Hamada, S., Kontani, M., Hosono, H., Ono, H., Tanaka, T., Ooshima, T., Mitsunaga, T., Abe, I., FEMS Microbiol Lett., 143 (1), 35-40 (1996)]. Polyphenols and their derivatives are also used in the food industry as preservatives.
A large proportion of polyphenolic extracts on the market are mixtures of many species with different degrees of polymerization. It is not known for most products how the different components of mixtures are absorbed and distributed in the different systems and biological tissues. Often, some of the active molecules are lost due to their tendency to aggregate among themselves or with proteins, processes that cause their deactivation for example in the skin or the digestive system. Moreover, researchers found that not only polyphenols, especially oligomeric ones, have a general biological activity but also different fractions or individual species of oligomeres have differentiated biological potentials. Owing to the similarity of their physico-chemical properties, the individual compounds are difficult to purify. Moreover, normally the amount of a selected oligomeric compound in a complex mixture is small.
Thioacidolysis of procyanidines and prodelfinidines is used to establish the degree of polymerization of oligomeric mixtures [Rigaud, J., Pérez-Ilzarbe, J., Ricardo da Silva, J. M., Cheynier, V., J. Chromatogr., 540, 401-405 (1991); Prieur, C., Rigaud, J., Cheynier, V., Moutounet, M., Phytochemistry, 36 (3), 781-784 (1994); Souquet, J.-M., Cheynier, V., Brossaud, F., Moutounet, M., Phytochemistry, 43 (2), 509-512 (1996), Souquet, J. M., Labarbe, B., LeGuerneve, C., Cheynier, V., Moutounet, M., J Agr. Food Chem., 48 (4), 1076-1080 (2000)]. Toluene-α-thiol is used as a source of thiols. Terminal flavan-3-ols are released as such while the internal polymer units are released as benzylthioethers in position 4 of the flavanolic system. The mixtures are studied by reverse phase high performance liquid chromatography, RP-HPLC). This method is useful from an analytical perspective. Applications have not been described for the resulting derivatives and also the breakdown product, Toluene-α-thiol, is toxic, irritant and lacrimogenous. The purification procedure only consists of reverse phase chromatography.
There is one example of cysteamine conjugates with an antioxidant molecule (tocopherol) [Pelle, E., Maes, D. H., U.S. Pat. No. 5,811,083]. Cysteamine is joined to tocopherol by an amide bond thus eliminating the amino function. Moreover, tocopherol is a different type of compound to flavan-3-ols. There are also examples of antioxidant compounds obtained by adding mercaptoethanol and alkylic chains to flavanols [Tanaka, T., Kusano, R., Kouno, I., Bioorg. Medicinal Chem. Letter, 8 (14), 1801-1806 (1998)]. These are derivatives that do not contain the amino group and have an amphyphylic character.